Laminins in the adult and aged brain

Exploring the properties and potential of the neural extracellular matrix for next-generation regenerative therapies

The extracellular matrix (ECM) is a dynamic and complex network of proteins and molecules that surrounds cells and tissues in the nervous system and orchestrates a myriad of biological functions. This review carefully examines the diverse interactions between cells and the ECM, as well as the transformative chemical and physical changes that the ECM undergoes during neural development, aging, and disease. These transformations play a pivotal role in shaping tissue morphogenesis and neural activity, thereby influencing the functionality of the central nervous system (CNS). In our comprehensive review, we describe the diverse behaviors of the CNS ECM in different physiological and pathological scenarios and explore the unique properties that make ECM-based strategies attractive for CNS repair and regeneration. Addressing the challenges of scalability, variability, and integration with host tissues, we review how advanced natural, synthetic, and combinatorial matrix approaches enhance biocompatibility, mechanical properties, and functional recovery. Overall, this review highlights the potential of decellularized ECM as a powerful tool for CNS modeling and regenerative purposes and sets the stage for future research in this exciting field. This article is categorized under: Implantable Materials and Surgical Technologies > Nanotechnology in Tissue Repair and Replacement Therapeutic Approaches and Drug Discovery > Nanomedicine for Neurological Disease Implantable Materials and Surgical Technologies > Nanomaterials and Implants.

In silico-in vitro modeling to uncover cues involved in establishing microglia identity: TGF-β3 and laminin can drive microglia signature gene expression

Microglia are the resident macrophages of the central nervous system (CNS) and play a key role in CNS development, homeostasis, and disease. Good in vitro models are indispensable to study their cellular biology, and although much progress has been made, in vitro cultures of primary microglia still only partially recapitulate the transcriptome of in vivo microglia. In this study, we explored a combination of in silico and in vitro methodologies to gain insight into cues that are involved in the induction or maintenance of the ex vivo microglia reference transcriptome. First, we used the in silico tool NicheNet to investigate which (CNS-derived) cues could underlie the differences between the transcriptomes of ex vivo and in vitro microglia. Modeling on basis of gene products that were found to be upregulated in vitro, predicted that high mobility group box 2 (HMGB2)- and interleukin (IL)-1β-associated signaling pathways were driving their expression. Modeling on basis of gene products that were found to be downregulated in vitro, did not lead to predictions on the involvement of specific signaling pathways. This is consistent with the idea that in vivo microenvironmental cues that determine microglial identity are for most part of inhibitory nature. In a second approach, primary microglia were exposed to conditioned medium from different CNS cell types. Conditioned medium from spheres composed of microglia, oligodendrocytes, and radial glia, increased the mRNA expression levels of the microglia signature gene P2RY12. NicheNet analyses of ligands expressed by oligodendrocytes and radial glia predicted transforming growth factor beta 3 (TGF-β3) and LAMA2 as drivers of microglia signature gene expression. In a third approach, we exposed microglia to TGF-β3 and laminin. In vitro exposure to TGF-β3 increased the mRNA expression levels of the microglia signature gene TREM2. Microglia cultured on laminin-coated substrates were characterized by reduced mRNA expression levels of extracellular matrix-associated genes MMP3 and MMP7, and by increased mRNA expression levels of the microglia signature genes GPR34 and P2RY13. Together, our results suggest to explore inhibition of HMGB2- and IL-1β-associated pathways in in vitro microglia. In addition, exposure to TGF-β3 and cultivation on laminin-coated substrates are suggested as potential improvements to current in vitro microglia culture protocols.

Non-productive angiogenesis disassembles Aß plaque-associated blood vessels

The human Alzheimer's disease (AD) brain accumulates angiogenic markers but paradoxically, the cerebral microvasculature is reduced around Aß plaques. Here we demonstrate that angiogenesis is started near Aß plaques in both AD mouse models and human AD samples. However, endothelial cells express the molecular signature of non-productive angiogenesis (NPA) and accumulate, around Aß plaques, a tip cell marker and IB4 reactive vascular anomalies with reduced NOTCH activity. Notably, NPA induction by endothelial loss of presenilin, whose mutations cause familial AD and which activity has been shown to decrease with age, produced a similar vascular phenotype in the absence of Aß pathology. We also show that Aß plaque-associated NPA locally disassembles blood vessels, leaving behind vascular scars, and that microglial phagocytosis contributes to the local loss of endothelial cells. These results define the role of NPA and microglia in local blood vessel disassembly and highlight the vascular component of presenilin loss of function in AD.

A microfluidic cell-migration assay for the prediction of progression-free survival and recurrence time of patients with glioblastoma

Clinical scores, molecular markers and cellular phenotypes have been used to predict the clinical outcomes of patients with glioblastoma. However, their clinical use has been hampered by confounders such as patient co-morbidities, by the tumoral heterogeneity of molecular and cellular markers, and by the complexity and cost of high-throughput single-cell analysis. Here, we show that a microfluidic assay for the quantification of cell migration and proliferation can categorize patients with glioblastoma according to progression-free survival. We quantified with a composite score the ability of primary glioblastoma cells to proliferate (via the protein biomarker Ki-67) and to squeeze through microfluidic channels, mimicking aspects of the tight perivascular conduits and white-matter tracts in brain parenchyma. The assay retrospectively categorized 28 patients according to progression-free survival (short-term or long-term) with an accuracy of 86%, predicted time to recurrence and correctly categorized five additional patients on the basis of survival prospectively. RNA sequencing of the highly motile cells revealed differentially expressed genes that correlated with poor prognosis. Our findings suggest that cell-migration and proliferation levels can predict patient-specific clinical outcomes.

The Influence of Neuron-Extrinsic Factors and Aging on Injury Progression and Axonal Repair in the Central Nervous System

In the aging western population, the average age of incidence for spinal cord injury (SCI) has increased, as has the length of survival of SCI patients. This places great importance on understanding SCI in middle-aged and aging patients. Axon regeneration after injury is an area of study that has received substantial attention and made important experimental progress, however, our understanding of how aging affects this process, and any therapeutic effort to modulate repair, is incomplete. The growth and regeneration of axons is mediated by both neuron intrinsic and extrinsic factors. In this review we explore some of the key extrinsic influences on axon regeneration in the literature, focusing on inflammation and astrogliosis, other cellular responses, components of the extracellular matrix, and myelin proteins. We will describe how each element supports the contention that axonal growth after injury in the central nervous system shows an age-dependent decline, and how this may affect outcomes after a SCI.

Three-plane description of astroglial populations of OVLT subdivisions in rat: Tanycyte connections to distant parts of third ventricle

This study demonstrates glial and gliovascular markers of organon vasculosum laminae terminalis (OVLT) in three planes. The distribution of glial markers displayed similarities to the subfornical organ. There was an inner part with vimentin- and nestin-immunopositive glia whereas GFAP and the water-channel aquaporin 4 were found at the periphery. This separation indicates different functions of the two regions. The presence of nestin may indicate stem cell-capabilities whereas aquaporin 4 has been reported to promote the osmoreceptor function. Glutamine synthetase immunoreactivity was sparse like in the area postrema and subfornical organ. The laminin and β-dystroglycan immunolabelings altered along the vessels such as in the subfornical organ indicating altering gliovascular relations. The different subdivisions of OVLT received glial processes of different origins. The posterior periventricular zone contained short vimentin-immunopositive processes from the ependyma of the adjacent surface of the third ventricle. The lateral periventricular zone received forceps-like process systems from the anterolateral part of the third ventricle. Most interestingly, the "dorsal cap" received a mixed group of long GFAP- and vimentin-immunopositive processes from a distant part of the third ventricle. The processes may have two functions: a guidance for newly produced cells like radial glia in immature brain and/or a connection between distant parts of the third ventricle and OVLT.

Pericytic Laminin Maintains Blood-Brain Barrier Integrity in an Age-Dependent Manner

Brain pericytes synthesize and deposit laminin at the blood-brain barrier (BBB). The function of pericyte-derived laminin in BBB maintenance remains largely unknown. In a previous study, we generated pericytic laminin conditional knockout (PKO) mice, which developed BBB breakdown and hydrocephalus in a mixed genetic background. However, since hydrocephalus itself can compromise BBB integrity, it remains unclear whether BBB disruption in these mutants is due to loss of pericytic laminin or secondary to hydrocephalus. Here, we report that, in C57Bl6 dominant background, the PKO mice fail to show hydrocephalus, have a normal lifespan, and develop BBB breakdown in an age-dependent manner. Further mechanistic studies demonstrate that abnormal paracellular transport, enhanced transcytosis, decreased pericyte coverage, and diminished AQP4 level are responsible for BBB disruption in PKO mice. These results suggest that pericyte-derived laminin plays an indispensable and age-dependent role in the maintenance of BBB integrity under homeostatic conditions.

Postmortem immunohistochemical alterations following cerebral lesions: A possible pathohistological importance of the β-dystroglycan immunoreactivity

The frequency of cerebrovascular injuries raises the importance of their immunohistological investigation in postmortem materials. Most injuries involve the impairment of the blood-brain barrier. The barrier is maintained by the glio-vascular connections which break up following injuries. Some immunohistochemical alterations may refer to the impairment of the gliovascular connections. Laminin and the components of the dystroglycan complex show characteristic immunohistochemical alterations following various experimental injuries (stab wound, cryogenic lesion, arterial occlusions): immunoreactivity of β-dystroglycan, α-dystrobrevin and aquaporin 4 disappeared while that of utrophin and laminin appeared along the vessels, whereas α-syntrophin visualized the reactive astrocytes but not the resting ones. The aims of the present study were to investigate whether these post-lesion alterations: (i) are reproducible with immersive fixation, which is used in postmortem histology; (ii) are resistant to a postmortem delay before fixation; and (iii) are to be attributed to a direct effect of the lesion, or are mediated by processes occurring only in the living brain. Three models were investigated: (i) following lesions, some brains were fixed by transcardial perfusion, others by immersion; (ii) following lesions, the animals were decapitated and stored at room temperature for 8 or 16 h before fixation; and (iii) the lesions were performed after decapitation. Cryogenic lesions were performed by applying a dry ice cooled copper rod to the brain surface of ketamine-xylazine anesthetized rats. The immunohistochemical reactions were performed on free-floating sections cut with vibratome. Both immunoperoxidase and immunofluorescence methods were used. The fixation method - perfusive or immersive - did not change the post-lesion phenomena investigated. The postmortem delay did not influence the β-dystroglycan immunoreactivity, that is its lack delineated the area of the lesion. However, in the case of the other substances, various lengths of postmortem delay rendered the immunohistochemistry uninterpretable. The results suggest β-dystroglycan immunostaining could be applied in the neuropathology to detect cerebrovascular impairments.

Correlation Between Extravasation and Alterations of Cerebrovascular Laminin and β-Dystroglycan Immunoreactivity Following Cryogenic Lesions in Rats

The blood-brain barrier becomes "leaky" following lesions. Former studies revealed that following lesions the immunoreactivity of cerebrovascular laminin becomes detectable whereas that of β-dystroglycan disappears. These alterations may be indicators of glio-vascular decoupling that may result in the impairment of the blood-brain-barrier. This study investigates correlation between the post-lesion extravasation and the above-mentioned immunohistochemical alterations. Following cryogenic lesions, the survival periods lasted 5, 10, 30 minutes, 1 or 12 hours, or 1 day. Some brains were fixed immediately post-lesion. Immunofluorescent reactions were performed in floating sections. The extravasation was detected with immunostaining for plasma fibronectin and rat immunoglobulins. When the survival period was 30 minutes or longer, the area of extravasation corresponded to the area of altered laminin and β-dystroglycan immunoreactivities. Following immediate fixation some laminin immunoreactivity was already detected. The extravasation seemed to precede this early appearance of laminin immunoreactivity. The β-dystroglycan immunoreactivity disappeared later. When the extravasation spread into the corpus callosum, vascular laminin immunoreactivity appeared but the β-dystroglycan immunoreactivity persisted. It seems that extravasation separates the glial and vascular basal laminae, which results in the appearance of laminin immunoreactivity. The disappearance of β-dystroglycan immunoreactivity is neither a condition nor an inevitable consequence of the 2 other phenomena.

Intrinsic Response Towards Physiologic Stiffness is Cell-Type Dependent

In the continuous search for better tissue engineering scaffolds it has become increasingly clear that the substrate properties dramatically affect cell responses. Here we compared cells from a physiologically stiff tissue, melanoma, to cells isolated from a physiologically soft tissue, brain. We measured the cell line responses to laminin immobilized onto glass or polyacrylamide hydrogels tuned to have a Young's modulus ranging from 1 to 390 kPa. Single cells were analyzed for spreading area, shape, total actin content, actin-based morphological features and modification of immobilized laminin. Both cell types exhibited stiffness- and laminin concentration-dependent responses on polyacrylamide and glass. Melanoma cells exhibited very little spreading and were rounded on soft (1, 5, and 15 kPa) hydrogels while cells on stiff (40, 100, and 390 kPa) hydrogels were spread and had a polarized cell shape with large lamellipodia. On rigid glass surfaces, spreading and actin-based morphological features were not observed until laminin concentration was much higher. Similarly, increased microglia cell spreading and presence of actin-based structures were observed on stiff hydrogels. However, responses on rigid glass surfaces were much different. Microglia cells had large spreading areas and elongated shapes on glass compared to hydrogels even when immobilized laminin density was consistent on all gels. While cell spreading and shape varied with Young's modulus of the hydrogel, the concentration of f-actin was constant. A decrease in laminin immunofluorescence was associated with melanoma and microglia cell spreading on glass with high coating concentration of laminin, indicating modification of immobilized laminin triggered by supraphysiologic stiffness and high ligand density. These results suggest that some cell lines are more sensitive to mechanical properties matching their native tissue environment while other cell lines may require stiffness and extracellular ligand density well above physiologic tissue before saturation in cell spreading, elongation and cytoskeletal re-organization are reached.

Regulation of Integrin α6 Recycling by Calcium-independent Phospholipase A2 (iPLA2) to Promote Microglia Chemotaxis on Laminin

Microglia are the immune effector cells that are activated in response to pathological changes in the central nervous system. Microglial activation is accompanied by the alteration of integrin expression on the microglia surface. However, changes of integrin expression upon chemoattractant (ADP) stimulation still remain unknown. In this study, we investigated whether ADP induces the alteration of integrin species on the cell surface, leading to changes in chemotactic ability on different extracellular matrix proteins. Flow cytometry scans and on-cell Western assays showed that ADP stimulation induced a significant increase of α6 integrin-GFP, but not α5, on the surface of microglia cells. Microglia also showed a greater motility increase on laminin than fibronectin after ADP stimulation. Time lapse microscopy and integrin endocytosis assay revealed the essential role of calcium-independent phospholipase A₂ activity for the recycling of α6 integrin-GFP from the endosomal recycling complex to the plasma membrane. Lack of calcium-independent phospholipase A₂ activity caused a reduced rate of focal adhesion formation on laminin at the leading edge. Our results suggest that the alteration of integrin-mediated adhesion may regulate the extent of microglial infiltration into the site of damage by controlling their chemotactic ability.

Glial and perivascular structures in the subfornical organ: distinguishing the shell and core

The subfornical organ (SFO) is a circumventricular organ with a chemosensitive function, and its vessels have no blood-brain barrier. Our study investigated the glial and vascular components in the SFO to determine whether their distributions indicate subdivisions, how to characterize the vessels and how to demarcate the SFO. To this end, we investigated glial markers (GFAP, glutamine synthetase, S100) and other markers, including vimentin and nestin (immature glia), laminin (basal lamina), β-dystroglycan (glio-vascular connections), and aquaporin 4 (glial water channels). We determined that the 'shell' of the SFO was marked by immunoreactivity for S100, GFAP and aquaporin 4. Nestin immunoreactivity was characteristic of the 'core'. Vimentin was almost evenly distributed. Glutamine synthetase immunoreactivity occurred in the shell but its expression was sparse. Vessels in the core were decorated with laminin but showed a discontinuous expression of aquaporin 4. Vimentin and GFAP staining was usually in separate glial elements, which may be related to their functional differences. Similar to other vessels in the brain, β-dystroglycan was detected along the shell vessels but laminin was not. The gradual disappearance of the laminin immunopositivity was attributed to the gradual disappearance of the perivascular space. Thus, our findings suggest that the shell and core glio-vascular structures are adapted to different sensory functions: osmoperception and the perception of circulating peptides, respectively.

The Cerebrovascular Basement Membrane: Role in the Clearance of β-amyloid and Cerebral Amyloid Angiopathy

Cerebral amyloid angiopathy (CAA), the accumulation of β-amyloid (Aβ) peptides in the walls of cerebral blood vessels, is observed in the majority of Alzheimer’s disease (AD) brains and is thought to be due to a failure of the aging brain to clear Aβ. Perivascular drainage of Aβ along cerebrovascular basement membranes (CVBMs) is one of the mechanisms by which Aβ is removed from the brain. CVBMs are specialized sheets of extracellular matrix that provide structural and functional support for cerebral blood vessels. Changes in CVBM composition and structure are observed in the aged and AD brain and may contribute to the development and progression of CAA. This review summarizes the properties of the CVBM, its role in mediating clearance of interstitial fluids and solutes from the brain, and evidence supporting a role for CVBM in the etiology of CAA.

Carboxymethylcellulose hydrogels support central nervous system-derived tumor-cell chemotactic migration: Comparison with conventional extracellular matrix macromolecules

The local microenvironment plays an important role in maintaining the dynamics of the extracellular matrix and the cell–extracellular matrix relationship. The extracellular matrix is a complex network of macromolecules with distinct mechanical and biochemical characteristics. Disruptions in extracellular matrix homeostasis are associated with the onset of cancer. The extracellular matrix becomes highly disorganized, and the cell–matrix relationship changes, resulting in altered cell-signaling processes and metastasis. Medulloblastoma is one of the most common malignant pediatric brain tumors in the United States. In order to gain a better understanding of the interplay between cell–extracellular matrix interactions and cell-migratory responses in tumors, eight different matrix macromolecule formulations were investigated using a medulloblastoma-derived cell line: poly-d-lysine, matrigel, laminin, collagen 1, fibronectin, a 10% blend of laminin–collagen 1, a 20% blend of laminin–collagen 1, and a cellulose-derived hydrogel, carboxymethylcellulose. Over time, the average changes in cell morphology were quantified in 2D and 3D, as was migration in the presence and absence of the chemoattractant, epidermal growth factor. Data revealed that carboxymethylcellulose allowed for a cell–extracellular matrix relationship typically believed to be present in tumors, with cells exhibiting a rounded, amoeboid morphology consistent with chemotactic migration, while the other matrices promoted an elongated cell shape as well as both haptotactic and chemotactic motile processes. Therefore, carboxymethylcellulose hydrogels may serve as effective platforms for investigating central nervous system-derived tumor-cell migration in response to soluble factors.

Glia unglued: how signals from the extracellular matrix regulate the development of myelinating glia

The health and function of the nervous system relies on glial cells that ensheath neuronal axons with a specialized plasma membrane termed myelin. The molecular mechanisms by which glial cells target and enwrap axons with myelin are only beginning to be elucidated, yet several studies have implicated extracellular matrix proteins and their receptors as being important extrinsic regulators. This review provides an overview of the extracellular matrix proteins and their receptors that regulate multiple steps in the cellular development of Schwann cells and oligodendrocytes, the myelinating glia of the PNS and CNS, respectively, as well as in the construction and maintenance of the myelin sheath itself. The first part describes the relevant cellular events that are influenced by particular extracellular matrix proteins and receptors, including laminins, collagens, integrins, and dystroglycan. The second part describes the signaling pathways and effector molecules that have been demonstrated to be downstream of Schwann cell and oligodendroglial extracellular matrix receptors, including FAK, small Rho GTPases, ILK, and the PI3K/Akt pathway, and the roles that have been ascribed to these signaling mediators. Throughout, we emphasize the concept of extracellular matrix proteins as environmental sensors that act to integrate, or match, cellular responses, in particular to those downstream of growth factors, to appropriate matrix attachment.

Matrix metalloproteinase-12 deficiency ameliorates the clinical course and demyelination in Theiler's murine encephalomyelitis

Matrix metalloproteinases (MMPs) are a family of extracellular proteases involved in the pathogenesis of demyelinating diseases like multiple sclerosis (MS). The aim of the present study was to investigate whether MMPs induce direct myelin degradation, leukocyte infiltration, disruption of the blood-brain barrier (BBB), and/or extracellular matrix remodeling in the pathogenesis of Theiler's murine encephalomyelitis (TME), a virus-induced model of MS. During the demyelinating phase of TME, the highest transcriptional upregulation was detected for Mmp12, followed by Mmp3. Mmp12 (-/-) mice showed reduced demyelination, macrophage infiltration, and motor deficits compared with wild-type- and Mmp3 knock-out mice. However, BBB remained unaltered, and the amount of extracellular matrix deposition was similar in knock-out mice and wild-type mice. Furthermore, stereotaxic injection of activated MMP-3, -9, and -12 into the caudal cerebellar peduncle of adult mice induced a focally extensive primary demyelination prior to infiltration of inflammatory cells, as well as a reduction in the number of oligodendrocytes and a leakage of BBB. All these results demonstrate that MMP-12 plays an essential role in the pathogenesis of TME, most likely due to its primary myelin- or oligodendrocyte-toxic potential and its role in macrophage extravasation, whereas there was no sign of BBB damage or alterations to extracellular matrix remodeling/deposition. Thus, interrupting the MMP-12 cascade may be a relevant therapeutic approach for preventing chronic progressive demyelination.

Casting a net on dendritic spines: the extracellular matrix and its receptors

Dendritic spines are dynamic structures that accommodate the majority of excitatory synapses in the brain and are influenced by extracellular signals from presynaptic neurons, glial cells, and the extracellular matrix (ECM). The ECM surrounds dendritic spines and extends into the synaptic cleft, maintaining synapse integrity as well as mediating trans-synaptic communications between neurons. Several scaffolding proteins and glycans that compose the ECM form a lattice-like network, which serves as an attractive ground for various secreted glycoproteins, lectins, growth factors, and enzymes. ECM components can control dendritic spines through the interactions with their specific receptors or by influencing the functions of other synaptic proteins. In this review, we focus on ECM components and their receptors that regulate dendritic spine development and plasticity in the normal and diseased brain.

Disruption of central nervous system barriers in multiple sclerosis

The delicate microenvironment of the central nervous system (CNS) is protected by the blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier (BCB). These barriers function in distinct CNS compartments and their anatomical basis lay on the junctional proteins present in endothelial cells for the BBB and in the choroidal epithelium for the BCB. During neuroinflammatory conditions like multiple sclerosis (MS) and its murine model experimental autoimmune encephalomyelitis (EAE), activation or damage of the various cellular components of these barriers facilitate leukocyte infiltration leading to oligodendrocyte death, axonal damage, demyelination and lesion development. This manuscript will review in detail the features of these barriers under physiological and pathological conditions, particularly when focal immune activation promotes the loss of the BBB and BCB phenotype, the upregulation of cell adhesion molecules (CAMs) and the recruitment of immune cells.

Post-ischemic hypothermia attenuates loss of the vascular basement membrane proteins, agrin and SPARC, and the blood-brain barrier disruption after global cerebral ischemia

Vascular basement membrane (BM) stabilizes brain vessels and inhibits endothelial cell cycle. Cerebral ischemia causes BM breakdown with the loss of structural BM components including collagens and laminins. In this study, the expression changes of the BM proteoglycan agrin, and the non-structural BM constituent SPARC (BM-40, osteonectin), were studied in brain vessels after global cerebral ischemia. A transient 20-min forebrain ischemia followed by 1, 6 or 24 h of reperfusion was induced in adult Sprague-Dawley rats by combined bilateral common carotid artery occlusion and hypotension (42-45 mm Hg). In a separate group of animals, a mild (32 degrees C) post-ischemic hypothermia was induced for 6 h, starting immediately after ischemia. RNA from approximately 500 brain vessels (20-100 microm) extracted by laser-capture microdissection (LCM) microscopy was used to determine the expression of proteoglycans agrin and SPARC mRNAs by quantitative PCR (Q-PCR). Protein expression was determined by immunohistochemistry in adjacent tissue sections. The BBB permeability was assessed using (3)H-sucrose as an in vivo tracer and by examining fibrinogen immunoreactivity in tissue sections. A transient global brain ischemia resulted in a significant (ANOVA, p<0.05; 6 animals/group) reduction in agrin and SPARC mRNAs in LCM-captured brain vessels 24 h after reperfusion. A time-dependent loss of agrin and SPARC from the BM during reperfusion was also observed by immunochemistry. A 6-h post-ischemic hypothermia reduced SPARC and agrin mRNA and protein losses, BBB transfer constant for (3)H-sucrose as well as fibrinogen extravasation 24 h after reperfusion. It is conluded that a transient post-ischemic hypothermia stabilizes brain vessels and reduces BBB disruption in part by preventing proteolytic degradation of regulatory BM constituents, SPARC and agrin.

Proteolytic fragments of laminin promote excitotoxic neurodegeneration by up-regulation of the KA1 subunit of the kainate receptor

Degradation of the extracellular matrix (ECM) protein laminin contributes to excitotoxic cell death in the hippocampus, but the mechanism of this effect is unknown. To study this process, we disrupted laminin gamma1 (lamgamma1) expression in the hippocampus. Lamgamma1 knockout (KO) and control mice had similar basal expression of kainate (KA) receptors, but the lamgamma1 KO mice were resistant to KA-induced neuronal death. After KA injection, KA1 subunit levels increased in control mice but were unchanged in lamgamma1 KO mice. KA1 levels in tissue plasminogen activator (tPA)-KO mice were also unchanged after KA, indicating that both tPA and laminin were necessary for KA1 up-regulation after KA injection. Infusion of plasmin-digested laminin-1 into the hippocampus of lamgamma1 or tPA KO mice restored KA1 up-regulation and KA-induced neuronal degeneration. Interfering with KA1 function with a specific anti-KA1 antibody protected against KA-induced neuronal death both in vitro and in vivo. These results demonstrate a novel pathway for neurodegeneration involving proteolysis of the ECM and KA1 KA receptor subunit up-regulation.

Laminins in peripheral nerve development and muscular dystrophy

Laminins are extracellular matrix (ECM) proteins that play an important role in cellular function and tissue morphogenesis. In the peripheral nervous system (PNS), laminins are expressed in Schwann cells and participate in their development. Mutations in laminin subunits expressed in the PNS and in skeleton muscle may cause peripheral neuropathies and muscular dystrophy in both humans and mice. Recent studies using gene knockout technology, such as cell-type specific gene targeting techniques, revealed that laminins and their receptors mediate Schwann cell and axon interactions. Schwann cells with disrupted laminin expression exhibit impaired proliferation and differentiation and also undergo apoptosis. In this review, we focus on the potential molecular mechanisms by which laminins participate in the development of Schwann cells.

TGF-beta1 suppresses T cell infiltration and VP2 puff B mutation enhances apoptosis in acute polioencephalitis induced by Theiler's virus

GDVII and DA strains of Theiler's murine encephalomyelitis virus (TMEV) differ in VP2 puff B. One week after GDVII virus infection, SJL/J mice had large numbers of TUNEL+ apoptotic cells with a relative lack of T cell infiltration in the brain. DA viruses with mutation in puff B induced higher levels of apoptosis than wild-type DA virus, but levels of inflammation in brains were similar between DA and DA virus mutants. The difference in inflammation among TMEVs could be due to TGF-beta1 expression that was seen only in GDVII virus infection and negatively correlated with CD3+ T cell infiltration.

Sialic acid residues on astrocytes regulate neuritogenesis by controlling the assembly of laminin matrices

In the developing nervous system migrating neurons and growing axons are guided by diffusible and/or substrate-bound cues, such as extracellular matrix-associated laminin. In a previous work we demonstrated that laminin molecules could self-assemble in two different manners, giving rise to matrices that could favor either neuritogenesis or proliferation of cortical precursor cells. We investigated whether the ability of astrocytes to promote neuritogenesis of co-cultivated neurons was modulated by the assembling mode of the laminin matrix secreted by them. We compared the morphologies and neuritogenic potentials of laminin deposited by in vitro-differentiated astrocytes obtained from embryonic or neonatal rat brain cortices. We showed that, while permissive astrocytes derived from embryonic brain produced a flat laminin matrix that remained associated to the cell surface, astrocytes derived from newborn brain secreted a laminin matrix resembling a fibrillar web that protruded from the cell plane. The average neurite lengths obtained for E16 neurons cultured on each astrocyte layer were 198+/-22 and 123+/-13 microm, respectively. Analyses of surface-associated electrostatic potentials revealed that embryonic astrocytes presented a pI of -2.8, while in newborn cells this value was -3.8. Removal of the sialic acid groups on the embryonic monolayer by neuraminidase treatment led to the immediate release of matrix-associated laminin. Interestingly, laminin reassembled 1 hour after neuraminidase removal converted to the features of the newborn matrix. Alternatively, treatment of astrocytes with the cholesterol-solubilizing detergent methyl-beta-cyclodextrin also resulted in release of the extracellular laminin. To test the hypothesis that sialic-acid-containing lipids localized at cholesterol-rich membrane domains could affect the process of laminin assembly, we devised a cell-free assay where laminin polymerization was carried out over artificial lipid films. Films of either a mixture of gangliosides or pure ganglioside GT1b induced formation of matrices of morpho-functional features similar to the matrices deposited by embryonic astrocytes. Conversely, films of phosphatidylcholine or ganglioside GM1 led to the formation of bulky laminin aggregates that lacked a defined structure. We propose that the expression of negative lipids on astrocytes can control the extracellular polymerization of laminin and, consequently, the permissivity to neuritogenesis of astrocytes during development.

Disappearance of the post-lesional laminin immunopositivity of brain vessels is parallel with the formation of gliovascular junctions and common basal lamina. A double-labelling immunohistochemical study

Previous studies revealed that during development the laminin immunopositivity gradually disappeared from the brain vessels, but temporarily re-appeared in them around lesions. The question of the present study was the correlation between the post-lesional vascular immunopositivity to laminin and the glial reaction. Following stab wounds, double fluorescent immunohistochemical labelling was performed against laminin (using a polyclonal antiserum against laminin 1) and glial fibrillary acidic protein. A number of vessels exhibited intense immunopositivity to laminin within the lesioned tissue. Where these laminin immunopositive vessels entered the perilesional brain substance, the astroglia formed contacts on them, and the separate vascular and glial basal laminae fused. The disappearance of the post-lesional laminin immunopositivity seemed to coincide with these phenomena. When monoclonal antibodies were applied against the beta1 and gamma1 laminin chains, vessels proved to be immunopositive at the lesion, but none in the intact brain tissue. No immunoreactivity was detected in the cases of alpha2 and beta2 chains. The results suggest that the disappearance of laminin immunopositivity may be attributed to that the epitopes become inaccessible for antibodies owing to the formation of gliovascular junctions and common basal lamina between astroglia and vessel. The possible role of an alteration in the laminin composition and the effect of fixation are discussed.

The hippocampal laminin matrix is dynamic and critical for neuronal survival

Laminins are extracellular matrix proteins that participate in neuronal development, survival, and regeneration. During excitotoxin challenge in the mouse hippocampus, neuron interaction with laminin-10 (alpha5,beta1,gamma1) protects against neuronal death. To investigate how laminin is involved in neuronal viability, we infused laminin-1 (alpha1,beta1,gamma1) into the mouse hippocampus. This infusion specifically disrupted the endogenous laminin layer. This disruption was at least partially due to the interaction of the laminin-1 gamma1 chain with endogenous laminin-10, because infusion of anti-laminin gamma1 antibody had the same effect. The disruption of the laminin layer by laminin-1 1) did not require the intact protein because infusion of plasmin-digested laminin-1 gave similar results; 2) was posttranscriptional, because there was no effect on laminin mRNA expression; and 3) occurred in both tPA(-/-) and plasminogen(-/-) mice, indicating that increased plasmin activity was not responsible. Finally, although tPA(-/-) mice are normally resistant to excitotoxin-induced neurodegeneration, disruption of the endogenous laminin layer by laminin-1 or anti-laminin gamma1 antibody renders the tPA(-/-) hippocampal neurons sensitive to kainate. These results demonstrate that neuron interactions with the deposited matrix are not necessarily recapitulated by interactions with soluble components and that the laminin matrix is a dynamic structure amenable to modification by exogenous molecules.

Genetic loci contributing to age-related hippocampal lesions in mice

C57BL/6J mice develop genetically determined age-related hippocampal granular deposits that have some similarities to lesions seen in the brains of human patients with tau protein related neurodegenerative disorders ("tauopathies"). We sought to identify the genetic loci responsible for these in an F2 intercross of inbred mouse strains C57BL/6J and DBA/2J, using quantitative trait locus (QTL) analysis. Hippocampal lesions were shown to be PAS positive, H and E negative, and immunoreactive for tau protein and alpha synuclein, but not to Abeta 1-40 or Abeta 1-42, or for ubiquitin. These were quantitated by histomorphometry, and QTL analysis revealed a locus on chromosome 7 with a lod score of 6.5 as well as two suggestive loci on chromosome 10. The genomic data indicate that the genetic basis is complex, but with one locus playing a major role in lesion formation. These lesions may represent a useful model for investigating dysregulation of tau protein in the hippocampus.

Integrins are involved in synaptogenesis, cell spreading, and adhesion in the postnatal brain

Integrins are a major family of heterodimeric surface glycoproteins that act as adhesion molecules, have a spectrum of extracellular matrix (ECM) molecules as their ligands, and regulate a variety of cellular functions. Integrins are known to be critical to embryonic brain development, and recent studies have indicated their essential role in adult brain function, although their role in postnatal brain development and function has not been examined. Here, we used the organotypic slice culture system to investigate the role of integrins in postnatal hippocampal development by exposing the tissue to either an integrin competitive antagonist, the peptide GRGDSP containing Arg-Gly-Asp (RGD) attachment site, or to function-blocking beta(1)-integrin antibodies to disrupt integrin interactions. These experiments revealed that beta(1)-integrin antibodies interfered with spreading of the culture, resulting in a rapid and marked diminution of slice area. beta(1)-integrin antibodies and RGD peptide disrupted cell adhesion, causing cell detachment and migration of glial cells from the explant. The majority of the detached cells were of macroglial origin and switched to expression of the intermediate filament proteins vimentin and nestin, suggesting a developmental regression. The organotypic organization of slice cultures was not affected, although exposure to either integrin antagonist or antibody resulted in a statistically significant reduction in the number of synapses measured in the apical dendrites of CA1 pyramidal neurons. The results demonstrate that integrins markedly affect postnatal CNS development, in both ultrastructural construction and organizational processes.

Laminin affects polymerization, depolymerization and neurotoxicity of Abeta peptide

Amyloid deposition in Alzheimer fibrils forms neurotoxic senile plaques in a process that may be modulated by associated proteins. In this work we demonstrate the ability of laminin-1 and laminin-2 to inhibit fibril formation and toxicity on cultured rat hippocampal neurons. We confirm that the laminin-1-derived peptide YFQRYLI inhibits efficiently both fibril formation and neurotoxicity and show that the IKVAV peptide inhibits amyloid neurotoxicity despite its slight inhibition of fibril formation. On other hand, laminin-1 induces disaggregation of preformed fibrils in vitro, characterized as a progressive disassembly of fibrils into protofibrils and further clearance of these latter species, leading to a continual inhibition of amyloid neurotoxicity.

Cerebral microvascular pathology in aging and Alzheimer's disease

The aging of the central nervous system and the development of incapacitating neurological diseases like Alzheimer's disease (AD) are generally associated with a wide range of histological and pathophysiological changes eventually leading to a compromised cognitive status. Although the diverse triggers of the neurodegenerative processes and their interactions are still the topic of extensive debate, the possible contribution of cerebrovascular deficiencies has been vigorously promoted in recent years. Various forms of cerebrovascular insufficiency such as reduced blood supply to the brain or disrupted microvascular integrity in cortical regions may occupy an initiating or intermediate position in the chain of events ending with cognitive failure. When, for example, vasoconstriction takes over a dominating role in the cerebral vessels, the perfusion rate of the brain can considerably decrease causing directly or through structural vascular damage a drop in cerebral glucose utilization. Consequently, cerebral metabolism can suffer a setback leading to neuronal damage and a concomitant suboptimal cognitive capacity. The present review focuses on the microvascular aspects of neurodegenerative processes in aging and AD with special attention to cerebral blood flow, neural metabolic changes and the abnormalities in microvascular ultrastructure. In this context, a few of the specific triggers leading to the prominent cerebrovascular pathology, as well as the potential neurological outcome of the compromised cerebral microvascular system are also going to be touched upon to a certain extent, without aiming at total comprehensiveness. Finally, a set of animal models are going to be presented that are frequently used to uncover the functional relationship between cerebrovascular factors and the damage to neural networks.

A stoichiometric complex of neurexins and dystroglycan in brain

In nonneuronal cells, the cell surface protein dystroglycan links the intracellular cytoskeleton (via dystrophin or utrophin) to the extracellular matrix (via laminin, agrin, or perlecan). Impairment of this linkage is instrumental in the pathogenesis of muscular dystrophies. In brain, dystroglycan and dystrophin are expressed on neurons and astrocytes, and some muscular dystrophies cause cognitive dysfunction; however, no extracellular binding partner for neuronal dystroglycan is known. Regular components of the extracellular matrix, such as laminin, agrin, and perlecan, are not abundant in brain except in the perivascular space that is contacted by astrocytes but not by neurons, suggesting that other ligands for neuronal dystroglycan must exist. We have now identified alpha- and beta-neurexins, polymorphic neuron-specific cell surface proteins, as neuronal dystroglycan receptors. The extracellular sequences of alpha- and beta-neurexins are largely composed of laminin-neurexin-sex hormone-binding globulin (LNS)/laminin G domains, which are also found in laminin, agrin, and perlecan, that are dystroglycan ligands. Dystroglycan binds specifically to a subset of the LNS domains of neurexins in a tight interaction that requires glycosylation of dystroglycan and is regulated by alternative splicing of neurexins. Neurexins are receptors for the excitatory neurotoxin alpha-latrotoxin; this toxin competes with dystroglycan for binding, suggesting overlapping binding sites on neurexins for dystroglycan and alpha-latrotoxin. Our data indicate that dystroglycan is a physiological ligand for neurexins and that neurexins' tightly regulated interaction could mediate cell adhesion between brain cells.

Integrin signaling via the PI3-kinase-Akt pathway increases neuronal resistance to glutamate-induced apoptosis

Integrins are integral membrane proteins that mediate adhesive interactions of cells with the extracellular matrix and with other cells. Integrin engagement results in activation of intracellular signaling cascades that effect several different cellular responses including motility, proliferation and survival. Although integrins are known to provide cell survival signaling in various types of non-neuronal cells, the possibility that integrins modulate neuron survival has not been explored. We now report data demonstrating a neuroprotective function of integrins in embryonic hippocampal neurons. Neurons grown on laminin, an integrin ligand, exhibit increased resistance to glutamate-induced apoptosis compared with neurons grown on polylysine. Neurons expressed integrin beta1 and treatment of cultures with an antibody against integrin beta1 abolished the protective effect of laminin. Neurons maintained on laminin exhibited a sustained activation of the Akt signaling pathway demonstrated in immunoblot analyses using an antibody that selectively recognizes phosphorylated Akt. The neuroprotective effect of integrin engagement by laminin was mimicked by an IKLLI-containing integrin-binding peptide and was abolished by treatment of neurons with the PI3 kinase inhibitor wortmanin. Levels of the anti-apoptotic protein Bcl-2 were increased in neurons grown on laminin and decreased by wortmanin, suggesting a mechanism for the neuroprotective effect of integrin-mediated signaling. The ability of integrin-mediated signaling to prevent glutamate-induced apoptosis suggests a mechanism whereby neuron-substrate interactions can promote neuron survival under conditions of glutamate receptor overactivation.

Suppression of nidogen-1 translation by antisense targeting affects the adhesive properties of cultured astrocytes

The multidomain glycoprotein nidogen-1 is a common component of basal membranes. Nidogen-1 is produced by the endothelial cells and the mesenchymal cells of the developing central nervous system. Recent results give evidence that nidogen-1 may also be secreted by cultured Schwann cells to basement membranes of peripheral nerves. We were interested in ascertaining whether astrocytes, which have the capacity to produce laminin and fibronectin and are an important source of extracellular matrix (ECM) molecule secretion in the brain, might also produce nidogen-1. Immunocytochemistry, in combination with polymerase chain reaction and in situ hybridization techniques, revealed that astrocytes in culture synthesize nidogen-1. To show the functional significance of the nidogen-1 secretion by astrocytes, antisense targeting techniques were applied. These experiments showed that nidogen-1 may be an essential modulator of astrocytic adhesion to the substrate. The suppression of nidogen-1 synthesis by the application of antisense oligonucleotides induced a morphological transition from a flat, polygonal to a round cell and was accompanied by the detachment of the astrocytes from the substrate. Hence, nidogen-1 might be an important component of the ECM secreted by astrocytes. The suppression of nidogen-1 synthesis may disturb the aggregation of ECM molecules to a functional basement membrane and thus reduce the astrocytic adhesion to the substrate. Nidogen-1 secretion to basement membranes by astrocytes may have important functional implications during blood-brain barrier and scar formation.

Laminin 1 attenuates beta-amyloid peptide Abeta(1-40) neurotoxicity of cultured fetal rat cortical neurons

A growing amount of evidence indicates the involvement of extracellular matrix components, especially laminins, in the development of Alzheimer's disease, although their role remains unclear. In this study, we clearly demonstrate that laminin 1 inhibits beta-amyloid peptide (Abeta)-induced neuronal cell death by preventing the fibril formation and interaction of the Abeta peptide with cell membranes. The presence of laminin at a laminin/Abeta peptide molar ratio of 1:800 significantly inhibits the Abeta-induced apoptotic events, together with inhibition of amyloid fibril formation. The inhibitory effects of laminin 1 were time- and dose-dependent, whereas laminin 2 had less effect on Abeta neurotoxicity. A preincubation of laminin and Abeta was not required to observe the protective effect of laminin, suggesting a direct interaction between laminin 1 and Abeta. Moreover, laminin had no effect on the toxicity of the fibrillar Abeta peptide, suggesting an interaction of laminin with nonfibrillar species of the Abeta peptide, sequestering the peptide in a soluble form. These data extend our understanding of laminin-dependent binding of Abeta and highlight the possible modulation role of laminin regarding Abeta aggregation and neurotoxicity in vivo.

Characterization and expression of the laminin gamma3 chain: a novel, non-basement membrane-associated, laminin chain

Laminins are heterotrimeric molecules composed of an alpha, a beta, and a gamma chain; they have broad functional roles in development and in stabilizing epithelial structures. Here, we identified a novel laminin, composed of known alpha and beta chains but containing a novel gamma chain, gamma3. We have cloned gene encoding this chain, LAMC3, which maps to chromosome 9 at q31-34. Protein and cDNA analyses demonstrate that gamma3 contains all the expected domains of a gamma chain, including two consensus glycosylation sites and a putative nidogen-binding site. This suggests that gamma3-containing laminins are likely to exist in a stable matrix. Studies of the tissue distribution of gamma3 chain show that it is broadly expressed in: skin, heart, lung, and the reproductive tracts. In skin, gamma3 protein is seen within the basement membrane of the dermal-epidermal junction at points of nerve penetration. The gamma3 chain is also a prominent element of the apical surface of ciliated epithelial cells of: lung, oviduct, epididymis, ductus deferens, and seminiferous tubules. The distribution of gamma3-containing laminins on the apical surfaces of a variety of epithelial tissues is novel and suggests that they are not found within ultrastructurally defined basement membranes. It seems likely that these apical laminins are important in the morphogenesis and structural stability of the ciliated processes of these cells.

Neuronal degeneration and a decrease in laminin-like immunoreactivity is associated with elevated tissue-type plasminogen activator in the rat hippocampus after kainic acid injection

Tissue-type plasminogen activator (tPA) is a serine protease that converts the inactive precursor plasminogen to the active protease plasmin. In the central nervous system, tPA has been suggested to participate in plasticity, memory and the neuronal degeneration caused by excitotoxins, but its precise functions during these processes are still unclear. We show in this report that tPA antigen level and extracellular tPA activity increased in the hippocampus during the early stages of neuronal degeneration in the CA3 region following the injection of kainic acid (KA) into the lateral cerebral ventricles. The increase in tPA antigen level was transient and its peak was at 4 h after the injection. tPA activity was also increased 4 h after the injection, but it remained at a high level for more than 8 h. Histological zymography showed that the increase in tPA activity was mainly localized in the CA3 region. In the same region, the disappearance of interneuronal laminin-like immunoreactivity and atrophic changes in pyramidal neurons were observed 4 h after the injection of KA. These results suggested that such focal and transient increases in tPA synthesis and release, which result in the proteolysis of laminin through plasminogen activation, could be involved in the neuronal degeneration in the CA3 region after the injection of KA.

Laminin-like proteins are differentially regulated during cerebellar development and stimulate granule cell neurite outgrowth in vitro

The basement membrane glycoprotein laminin-1 is a potent stimulator of neurite outgrowth. Although a variety of laminin isoforms have been described in recent years, the role of alternative laminin isoforms in neural development remains largely uncharacterized. We found that a polyclonal antibody raised against the alpha1, beta1, and gamma1 chains of laminin-1 and a monoclonal antibody raised against the alpha2 chain of laminin-2 detect immunoreactive material in neuronal cell bodies in the developing mouse cerebellum. In addition, laminin-1-like immunoreactivity was found in cell types throughout the cerebellum, but laminin-alpha2-like immunoreactivity was restricted to the Purkinje cells. Purified laminin-1 and laminin-2 stimulated neurite outgrowth in primary cultures of mouse cerebellar granule neurons to a similar extent, whereas the synthetic peptides tested appeared to be active only for cell adhesion and not for stimulation of neurite outgrowth. The E8 proteolytic fragment of laminin-1 contained full neurite outgrowth activity. The identity of laminins expressed in granule neurons was also examined by Western blotting; laminin-like complexes were associated with the cell and appeared to have novel compositions. These results suggest that laminin-like complexes play important roles in cerebellar development.

Endothelial cell integrin laminin receptor expression in multiple sclerosis lesions

Laminin, a major glycoprotein component of vessel basement membranes, is recognized by beta1- and beta3-integrins expressed on endothelial cells. To determine how endothelial cell integrins might function in multiple sclerosis (MS) lesions, integrin laminin receptors and laminin were analyzed in central nervous system samples from MS patients and controls by immunohistochemistry. In active MS lesions, endothelial cell VLA-6 and beta1 subunits were decreased compared to controls whereas alpha(v) subunit and VLA-1 were increased. In chronic inactive lesions beta1, VLA-6 and alpha(v) were the same as controls but VLA-1 remained increased. Alpha3 subunit was constant in all samples. By immunoelectron microscopy VLA-1, VLA-6, beta1, and laminin were distributed throughout endothelial cells; alpha(v) was adjacent to and on luminal surfaces; alpha(v) and VLA-1 were on intercellular junctions. These results indicate distinct regulation and functions of these integrins in different lesion stages. In active lesions decreased endothelial cell beta1/VLA-6 could result in their detachment from laminin thereby facilitating leukocyte transvascular migration and blood-brain barrier breakdown. Alpha(v) and VLA-1 on intercellular junctions may participate in re-establishing vessel integrity after leukocyte migration. Luminal surface alpha(v) also likely binds intraluminal ligands and cells. In chronic inactive plaques persistently elevated endothelial cell VLA-1 correlates with long-standing endothelial cell and blood-brain barrier dysfunction.

Differential expression of laminin chains in the human major salivary gland

Laminin represents a macromolecule family. The heterotrimeric isoforms of laminin can be determined by immunohistochemical demonstration of the single chains. The laminin chain heterogeneity of the basement membrane in adult human major salivary glands was evaluated in relation to cellular differentiation of the epithelia and the stromal compartment. Monoclonal antibodies to the laminin alpha1, alpha3 (BM165) chains and epiligrin reacted with the basement membranes of serous and mucous acini and of intercalated, striated and excretory ducts. As evidenced by a double-labelling technique, the alpha2 chain showed a spatial association with the myoepithelium of the acini, whereas the ductal basement membranes containing no myoepithelial cells were negative. Almost exclusively, beta1 chain was detected in acinar basement membrane, beta2 chain whereas in ductal basement membrane. Gamma2 chain is a unique chain belonging to the laminin-5 isoform. It was restricted to the ductal basement membrane. Alpha1, alpha2, beta1, beta2 and gamma1 chains were detected in nerves of salivary tissue and alpha1, alpha3, beta1, beta2 and gamma1 chains and epiligrin in blood vessels. Our results indicate that the acinar ductal unit contains basement membranes with different isoforms, which relate to cell differentiation and cell function.

Vascular basement membrane pathology and Alzheimer's disease

We have previously demonstrated that the capillary vascular basement membrane (VBM) is pathologically altered in Alzheimer's disease (AD). This microangiopathy is highlighted by the immunocytochemical localization of the three principal intrinsic VBM components: heparan sulfate proteoglycan, collagen type IV, and laminin. These three VBM components also immunolable amyloid deposits and senile plaque-associated glial processes. The present study examines the ultrastructure of the VBM in one brain region severely affected (temporal gyrus) and one relatively spared (cerebellum) from the lesions of AD in both AD and neurological control cases. The cross-sectional area as well as the width of the VBM were found to be greater in AD cortical capillaries. In addition, we found ultrastructural evidence for the activation of microglial-related perivascular cells, and their apparent extravasation through the VBM, findings consistent with the hypothesis that these cells are being recruited as part of a disease-related immune response. The recruitment of these "resting" microglial-like cells from their intra-VBM location to plaques and tangles in AD may explain (1) the thickening and vacuolization of the VBM; (2) the specificity of this VBM alteration to brain regions where there are plaques and tangles; and (3) the source of some of the large number of activated microglia in these affected areas. Thus, while VBM alterations may not be specific to AD, these changes appear to be specifically related to the disease process.

Laminins of the adult mammalian CNS; laminin-alpha2 (merosin M-) chain immunoreactivity is associated with neuronal processes

Laminins are glycoproteins with three subunits, i.e. a longer alpha chain, a shorter beta chain and a shorter gamma chain. Well-characterized laminins are laminin-1 (EHS laminin; alpha1-beta1-gamma1), laminin-2 (merosin; alpha2-beta1-gamma1), laminin-3 (alpha1-beta2-gamma1) and laminin-4 (alpha2-beta2-gamma1). The present study shows that in the adult mammalian CNS (rat, rabbit, pig and monkey) alpha2 chain immunoreactivity is associated most evidently with neuronal fibers and punctate, potentially synaptic, structures of limbic brain regions. Third ventricle tanycytes and ensheathing cells of the olfactory nerve also express intense alpha2 chain immunoreactivity. Immunostaining for gamma1 chain is present throughout the central nervous system (CNS) in essentially all neuronal cell bodies and their most proximal processes. Immunoreactivity for all chains investigated (alpha1, alpha2, beta1, beta2 and gamma1) were present around blood vessels, especially evident in lightly fixed tissues. The finding that, other than blood vessels, neurons and other structures exhibited immunoreactivity for only one or two (and not three) chains, suggests that variant forms of laminin with yet undiscovered chains or other configurations than the heterotrimeric form are present in the CNS. The association of alpha2-like immunoreactivity with neuronal fibers and synaptic structures is of great interest in light of the known neurite-promoting and cell attachment activities of laminin-2.

Dystroglycan in the cerebellum is a laminin alpha 2-chain binding protein at the glial-vascular interface and is expressed in Purkinje cells

Dystroglycan is a core component of the dystrophin receptor complex in skeletal muscle which links the extracellular matrix to the muscle cytoskeleton. Dystrophin, dystrophin-related protein (DRP, utrophin) and dystroglycan are present not only in muscles but also in the brain. Dystrophin is expressed in certain neuronal populations while DRP is associated with perivascular astrocytes. To gain insights into the function and molecular interactions of dystroglycan in the brain, we examined the localization of alpha- and beta-dystroglycan at the cellular and subcellular levels in the rat cerebellum. In blood vessels, we find alpha-dystroglycan associated with the laminin alpha 2-chain-rich parenchymal vascular basement membrane and beta-dystroglycan associated with the endfeet of perivascular astrocytes. We also show that alpha-dystroglycan purified from the brain binds alpha 2-chain-containing laminin-2. These observations suggest a dystroglycan-mediated linkage between DRP in perivascular astrocytic endfeet and laminin-2 in the parenchymal basement membrane similar to that described in skeletal muscle. This linkage of the astrocytic endfeet to the vascular basement membrane is likely to be important for blood vessel formation and stabilization and for maintaining the integrity of the blood-brain barrier. In addition to blood vessel labelling, we show that alpha-dystroglycan in the rat cerebellum is associated with the surface of Purkinje cell bodies, dendrites and dendritic spines. Dystrophin has previously been localized to the inner surface of the plasma membrane of Purkinje cells and is enriched at postsynaptic sites. Thus, the present results also support the hypothesis that dystrophin interacts with dystroglycan in cerebellar Purkinje neurons.